When applying equipment characteristics to a container, it is preferable to securely hold the container. Typically, one holds the container between a container support and either a centering element or a centering cone that lies against the container opening. The container support then causes a controlled rotation of the container about a vertical container axis.
In many cases it is necessary to label or print on thin-walled empty containers. Examples include thin-walled plastic or PET containers, including bottles. Such containers are often made by blow molding. Because these containers have low inherent stability, it is useful to pre-tension them with gas. The high pressure gas supports the walls so that the bottles are neither deformed nor destroyed by the container clamping force needed to apply the equipment characteristics.
Known pre-tensioning methods feature having a centering cone form a tight seal against the container mouth and having the centering element opening a control valve to let in high pressure gas. The pressure is usually generated by cam control with in each case an actuation element or linkage interacting with a control cam. The element or linkage acts on the centering element via a pressure spring. As a result, the pressure or container clamping force acting between the centering element and the container rises suddenly immediately after lowering the centering element onto the container. Since this occurs before high-pressure gas has stabilized the container, container damage can result.
In known labeling machines, a control disk opens the control valve for the pressure medium depending on the rotary position of the rotor. This makes it possible to dispense support medium even when there is no container at the relevant treatment position.
In labeling machines, it is also known to make the centering elements so that actuating the control valve to release the pressure medium takes place by the particular container and by raising the centering cone of the centering element. The force needed for this is, however, determined by the pressure of the support medium. As container walls become ever thinner, they become increasingly unstable when empty. This results in a considerable disadvantage. Loading the containers with an elevated internal pressure that stabilizes them means that a high force is needed between the container and the centering cone when the container is still not sufficiently stabilized.